/* ------------------------------------------------------------------------ */
// ISR function to read the analog pins.
/* ------------------------------------------------------------------------ */
ISR(ADC_vect)
{
    BITS_CLEAR(ADCSRA, ADSC);
    uint8_t adc_low = ADCL;
    // read adc1, and set next channel as adc2
    if (adc_i == 1) {
        adc_i++;
        adc_1_value = ((ADCH <<8) | adc_low);
        // MUX:0010  -> ADC2
        BITS_CLEAR(ADMUX, MUX0);
        BITS_SET(ADMUX, MUX1);
    }
    else if (adc_i == 2) {
        adc_i++;
        adc_2_value = ((ADCH <<8) | adc_low);
        // MUX:0011  -> ADC3
        BITS_SET(ADMUX, MUX0);
    // read adc3, and set next channel as adc1
    }
    else if (adc_i == 3) {
        adc_i = 1;
        adc_3_value = ((ADCH <<8) | adc_low);
        // MUX:0001 -> ADC1
        BITS_CLEAR(ADMUX, MUX1);
    }
    // start the adc measurements
    BITS_SET(ADCSRA, ADSC);
}